A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. If enough evidence accumulates to support a hypothesis, it moves to the next step—known as a theory—in the scientific method and becomes accepted as a valid explanation of a phenomenon.
When used in non-scientific context, the word “theory” implies that something is unproven or speculative. As used in science, however, a theory is an explanation or model based on observation, experimentation, and reasoning, especially one that has been tested and confirmed as a general principle helping to explain and predict natural phenomena.
Any scientific theory must be based on a careful and rational examination of the facts. In the scientific method, there is a clear distinction between facts, which can be observed and/or measured, and theories, which are scientists’ explanations and interpretations of the facts. Scientists can have various interpretations of the outcomes of experiments and observations, but the facts, which are the cornerstone of the scientific method, do not change.
A theory must include statements that have observational consequences. A good theory, like Newton’s theory of gravity, has unity, which means it consists of a limited number of problem-solving strategies that can be applied to a wide range of scientific circumstances. Another feature of a good theory is that it formed from a number of hypotheses that can be tested independently.
A scientific theory is not the end result of the scientific method; theories can be proven or rejected, just like hypotheses. Theories can be improved or modified as more information is gathered so that the accuracy of the prediction becomes greater over time.
Theories are foundations for furthering scientific knowledge and for putting the information gathered to practical use. Scientists use theories to develop inventions or find a cure for a disease.
A few theories do become laws, but theories and laws have separate and distinct roles in the scientific method. A theory is an explanation of an observed phenomenon, while a law is a description of an observed phenomenon.